The invention relates to a device for providing pipette tips.
Pipettes tips are small tubes made of plastic which are used in the laboratory for metering liquid samples, preferably within the range of 0.1 μL to 100 mL. They have a bottom opening for liquid and a top opening for air, and the cross-section of the pipette tips generally increases from the bottom opening toward the top opening.
To meter liquid, the top end of the pipette tip is connected to a pipette such that the top opening is joined to a pipette displacement device for air. The pipette tip with the opening is clamped onto a shoulder of the pipette, or clamped in a hole of the pipette. A channel terminates in the face of the shoulder or respectively in the base of the hole, and the channel is connected to the pipette displacement device. The displacement device of a piston stroke pipette is a cylinder with a piston which can move therein. With the assistance of the displacement device, an air volume is shifted such that a specific amount of liquid is drawn into the pipette tip and discharged therefrom. The metered amount of liquid depends on the displacement of the displacement device. Fixed volume pipettes with a constant metering volume have a constant displacement, and variable pipettes with an adjustable metering volume have an adjustable displacement. With direct displacement pipettes, a piston is integrated in the pipette tip which is driven by the displacement device.
After being used, the pipette tip is removed from its seat on the pipette, for which purpose the pipette can have an ejector that, upon being actuated, pushes the pipette tip off of its seat. Then the pipette can accommodate a new pipette tip. This prevents the carryover of sample liquid between sequential metering.
In order to affix pipette tips on the seat of a pipette, pipette tips are provided on devices for providing pipette tips. These devices have a plate-shaped carrier with a substantially rectangular surface made of plastic, also termed a tray or wafer, with a plurality of holes in a matrix arrangement. The perforated plate generally has 96 holes in 8 rows and 12 columns. Pipette tips are inserted from above into the holes, and they do not fall through the holes due to a diameter that is wider at the top or a collar at their top end.
Furthermore, these devices comprise a bottom part which is designed as a box that is closed at the bottom and open at the top, and a rectangular frame (also termed a “rack”) that is open at the bottom or the top. A carrier equipped with pipette tips is placeable on the top edge of the bottom part on means for supporting such that the pipette tips and the carrier extend into a seat in the bottom part. Known devices for providing pipette tips have a gripping tab on each of two opposing narrow sides of the carrier, the tabs being connected to the bottom edge of the narrow side of the carrier, having an actuating end at the top, and possessing a locking bead therebetween that locks with a locking projection on the inside of a side wall of the bottom part. The narrow sides are the two longitudinal sides and the two short sides of the rectangular carrier.
The pipette tips can be removed from a device for providing pipette tips by pressing the seat of a single channel pipette, or the seats of a multi-channel pipette, onto or into the top ends of the pipette tips, individually or several at the same time. The locked gripping tabs prevent the carrier from being unintentionally lifted while the pipette tips are being removed by a pipette.
Devices for providing pipette tips are known in which the bottom part can be reused after all of the pipette tips have been removed. To exchange the carrier, the lock can be released by pressing the gripping tabs toward each other and lifting the gripping tabs. The bottom part can be equipped with fresh pipette tips by means of refill packs. The refill packs comprise one or several plate-shaped carriers that are equipped with pipette tips. Refill packs are known, for example, with one or several carriers equipped with pipette tips arranged in folding boxes or cardboard frames, or in simple plastic boxes or plastic frames.
In order to equip the bottom part with a carrier with pipette tips from a refill pack, the user must precisely align the new carrier with the top opening of the bottom part and lower the new carrier with the pipette tips into the seat until the gripping tabs lock in the bottom part. It is difficult to correctly align the carrier equipped with pipette tips with the bottom part and find the locking position. Catching can occur which disturbs the process and prevents the finding of the locking position. If the carrier does not lock with the bottom part, the carrier can be lifted while seating pipette tips, and the pipette tips can consequently fall out. A further disadvantage is that the user cannot read product information affixed to one or more narrow sides of the carrier when the carrier is locked with the bottom part since the side walls of the bottom part cover the narrow sides. In order to read the product information, the user must release the lock and lift the carrier. If the product information is for example arranged on a label on the outside of the bottom part, there is no guarantee that it relates to the refilled pipette tips since it is possible that pipette tips of a different kind have been refilled.